A carbon nanotube (CNT) is one or more sheets of graphite rolled into a tube with a diameter on the order of a nanometer. Single-walled carbon nanotubes (SWNTs) consist of a single sheet of graphite with a thickness of roughly one atom, whereas multi-walled carbon nanotubes (MWNTs) consist of multiple sheets of graphite rolled into concentric tubes. In general, CNTs are an attractive option for electron emission given their robust physical, chemical and electrical properties. And in particular, CNTs perform well as cold field emitters due to their high aspect ratios providing low turn-on fields.
Given the robust properties of CNTs and their ability to emit electrons, CNTs can make very effective electron sources for electron field emission guns. However, the performance of the electron gun is dependent upon the implementation of the CNT within the electron gun, as well as the overall configuration of the electron gun itself. Most conventional electron guns utilize poor CNT implementation and electron gun configuration, and as such, exhibit poor field emission characteristics, stability, reliability, and durability.
For example, U.S. Pat. No. 7,151,268 to Fujieda et al. discusses a conventional electron gun using a conventional extractor to extract electrons from an electron source. The electron gun discussed in the '268 patent has no provision for aligning the CNT with the extractor, thereby requiring complex and expensive focusing electron optics. Additionally, the misalignment of the extractor and the CNT in conventional electron guns requires the use of large focusing electron optics. Accordingly, conventional electron guns cannot be used in many miniaturized applications.